Hydraulic accumulator

ABSTRACT

A hydraulic accumulator includes a piston ( 3 ) capable of moving in an accumulator housing ( 1 ) in its axial direction and separating a gas side ( 5 ) from a liquid side ( 7 ) of the accumulator housing ( 1 ). Guide elements ( 9, 17 ) designed to co-operate with the accumulator housing wall ( 1 ), as well as at least one sealing element ( 15 ), are arranged at the periphery of the piston. The sealing element is arranged offset in the axial direction relative to the guide elements ( 9, 17 ), and is located between the guide elements. In the piston ( 3 ), a pressure compensating channel ( 19 ) forms, at the piston periphery, a liquid flow path between the liquid side ( 7 ) and a space ( 2 ) located between the guide element ( 17 ) nearest to the liquid side ( 7 ) and the sealing element immediately next in the axial direction. A device ( 25 ) reducing the cross-section of the passage of the pressure compensating channel ( 19 ) is located in it.

FIELD OF THE INVENTION

The present invention relates to a hydraulic accumulator with a pistonwhich can be moved in the accumulator housing in its axial direction andwhich separates the gas side from the fluid side of the accumulatorhousing. On the periphery of the piston, guide elements are provided forinteraction with the wall of the accumulator housing. At least onesealing element, offset in the axial direction to the guide elements, islocated in the peripheral section of the piston situated between theguide elements.

BACKGROUND OF THE INVENTION

Piston accumulators are commercially available and are widely used inhydraulic systems in a variety of applications. For example, they areused for storing energy, emergency actuation, leaking oil compensation,volume compensation, shock absorption, pulsation damping, and the like.

Long-term behavior is of very great importance for economical andreliable use of these accumulators. To guarantee operating behaviorwhich is satisfactory in this regard, it must be ensured that the oiloverflow from the fluid side which normally contains hydraulic oil tothe gas side is minimized over the entire service life. Currenthydraulic accumulators do not meet this requirement to an adequatedegree.

DE 14 50 347 A discloses a generic hydraulic accumulator with a pistonwhich can be moved in the accumulator housing in its axial direction andwhich separates the gas side from the fluid side of the accumulatorhousing. The periphery of the piston has guide elements that interactwith the wall of the accumulator housing, together with at least onesealing element offset in the axial direction to the guide elements.Between the guide element nearest the piston side bordering on the fluidside and the sealing element which is offset in the axial direction tothe gas side and which is the next one following in the axial direction,a pressure equalization channel discharges on the periphery of thepiston and forms in the piston a fluid path to the fluid side. Thepressure equalization channel contains a device which reduces itspassage cross-section. In the known solution, the piston is formed fromtwo piston parts which are held at a distance to one another by anenergy accumulator in the form of a compression spring and which arerouted within the accumulator housing along a common guide rod forming astop.

Due to the motion of the overall piston within the accumulator housing,there is a pressure difference between the fluid side and theintermediate space which is located on the periphery of the pistonbetween the guide element on the fluid-side end of the piston and thesealing element which follows next in the axial direction. Due to thispressure difference, a volumetric flow into the intermediate spacebetween the guide element and sealing element occurs over the guideelement. Entrained dirt particles are deposited in this way between theguide element and the piston. Due to movement of the overall piston,these particles can lead to scratches which adversely affect the system.The described pressure equalization channel eliminates the problem inthat when the piston moves, no pressure difference occurs on the guideelement and thus a volumetric flow which may be loaded with dirtparticles is not produced. In the known solution it is possible thatwhen the piston moves, dirt particles which may have already collectedon the inside wall of the accumulator housing are run over in pistonmovements to damage the piston.

To prevent this problem, the prior art (DE 36 19 457 A) suggested acylindrical hydraulic accumulator for hydraulic systems, having anaccumulator housing cylinder closed on its two faces. A floating pistonin the housing cylinder divides the cylinder into two spaces. Towardsits seal against the inside cylinder wall on the two ends of its outsidewall, the piston has one recess each. In one recess, a respectivegroove-packing ring of elastomer is arranged, such that its annulargroove is pointed toward the pertinent piston face. However, thismeasure is not sufficient for effectively deterring dirt particles. Theknown groove-packing rings each have in cross-section a tetragonalprofile sectional area which undergoes transition toward the pertinentface of the piston into a U-shaped profile cross-sectional area. TheU-shaped profile cross-sectional area projects radially over thetetragonal profile cross-sectional area as a plain compression ring. Thetetragonal profile cross-sectional area in its entire width is enclosedby a support ring of a high-strength material, preferably of a carbonfiber winding bonded in resin, with an outer surface which adjoins theinside cylinder wall, sliding almost without play. In the U-profile areawhich is left clear, dirt can collect which can adversely affect thesealing function. The projecting angular stripper edge of the seal,which edge is configured to be solid, is designed too stiffly for aneffective sealing and stripping function.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved hydraulicaccumulator with a pressure equalization channel in the piston such thatimproved long-term operating behavior can be achieved.

In a hydraulic accumulator with a pressure equalization channel in thepiston, this object is achieved according to the present invention inthat the guide element nearest the fluid side of the piston is locatedclosely adjacent to the fluid-side end of the piston and is formed by aguide belt with a dirt stripper lip which extends at least approximatelyto the end of the piston. The guide belt has a plain compression ringwhich sits in an annular groove of the piston periphery with a dirtstripper lip which lengthens its radially outside annular surface on oneside in the axial direction and which tapers towards its end edge. Thepiston in the peripheral area which extends from the fluid-side end tothe annular groove has a section of reduced outside diameter over whichthe dirt stripper lip extends. In this way, dirt particles which mayhave already collected on the inside wall of the accumulator housing areprevented with certainty from being run over when the piston moves. Thestripper lip of the plain compression ring in particular alsocontributes to this prevention. The stripper lip extends tapering to theoutside and, located in the area of the piston end, extends preferablyover an axial length which is somewhat larger than half the axial lengthof the plain compression ring.

The device which reduces the passage cross-section of the pressureequalization channel ensures that only a small fluid volume is involvedin the process of pressure equalization.

The device which causes a reduction of the passage cross-section of thepressure equalization channel preferably reduces the passagecross-section so dramatically that as a result of the narrowing of thecross-section the action of a particle filter arises. Even a minimumvolumetric flow through the pressure equalization channel, as arises forpressure equalization during movements, does not lead to transport ofdirt particles into the intermediate space which is located downstreamof the guide element on the periphery of the piston.

The device which reduces the passage cross-section can be a chokedevice, for example a nozzle which is inserted into the pressureequalization channel, with a correspondingly small nozzle opening whichacts as a particle filter.

Instead of a choking nozzle as the device which narrows thecross-section, a porous filter element can be inserted into the pressureequalization channel.

Other objects, advantages and salient features of the present inventionwill become apparent from the following detailed description, which,taken in conjunction with the annexed drawings, discloses a preferredembodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which form a part of this disclosure:

FIG. 1 is a side elevational view in longitudinal section of a pistonaccumulator according to one exemplary embodiment of the presentinvention, where the section of the accumulator housing being shown isin which the piston is located; and

FIG. 2 is a partial side elevational view in longitudinal section of apiston guide element of the exemplary embodiment of FIG. 1, whichsection is drawn with a highly enlarged scale compared to FIG. 1, in theform of a plain compression ring with a projecting dirt stripper lip.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiment of the hydraulic accumulator according to thepresent invention is in the form of a piston accumulator. FIG. 1 showsonly the section of the accumulator housing 1 in which the piston 3 islocated. It forms a separating element which can move in the axialdirection, i.e., along the longitudinal axis 4, between the gas side 5and the fluid side 7 of the accumulator housing 1.

In hydraulic accumulators incorporated into hydraulic systems, the gasside 5 is conventionally filled with nitrogen gas, while the fluid side7 in operation conventionally contains hydraulic oil. The sealing andguidance system acts between the periphery of the piston 3 and theinside wall of the accumulator housing 1, prevents overflow of mediafrom one piston side to the other piston side, and forms a piston guidewhen the piston 3 is moving. Such system has a plurality of componentsprovided on the periphery of the piston 3. In succession, in FIG. 1 inthe axial direction from left to right, the components are a guideelement which is adjacent to the fluid-side end of the piston 3 in theform of a guide belt 9, a first piston seal 11 which is located at anaxial distance from guide belt 9 approximately in the central area ofthe piston 3, a second piston seal 15 which is further offset relativeto the first piston seal in the axial direction toward the fluid-sideend 13 of the piston 3, and a guide element which is still furtheroffset toward the end 13 of the piston 3 in the form of a guide belt 17.

As seen in the lower part of FIG. 1, a pressure equalization channel 19is in piston 3, and is formed from two blind holes which undergotransition into one another. One blind hole 20 proceeds from the end 13of the piston 3, and extends parallel to the longitudinal axis 4. Theother blind hole 21 extends at a right angle to blind hole 20, andproceeds from the periphery of the piston 3. Blind hole 21 on theperiphery of the piston discharges into an intermediate space 23 locatedbetween the guide belt 17 and the piston seal 15 extending therebetweenin the axial direction.

As a result of hydrodynamic circumstances, in operation when the piston3 moves a pressure difference arises between the space 23 and thepressure of the hydraulic oil located on the fluid side 7. This pressuredifference in the absence of a pressure equalization channel 19 leads toa slight volumetric flow over the guide belt 17. As already mentioned,entrained particles deposited between the inside wall of the housing 1and the piston 3 can lead to disruptions of the sealing and guidancesystem. The pressure equalization channel 19 of the present inventionavoids the formation of a corresponding pressure difference, and thus,the corresponding oil overflow.

To preclude the danger of a fluid flow, which occurs in the pressureequalization channel 19 during the process of pressure equalization andwhich is able to cause particles to be brought into the space 23, thepresent invention provides a narrowing of the passage cross-section ofthe channel 19.

In the embodiment shown in FIG. 1, this device is formed by a nozzle 25inserted into the mouth of the hole 20 of the channel 19 on the end 13of the piston 3. The nozzle hole 27 is chosen to be of such smalldimension here that it acts as a particle filter so that no particleswhich have a dimension greater than that of the hole 27 can travel intothe space 23 by way of the channel 19.

Instead of using a nozzle hole 27 of correspondingly small dimensions asa particle filter, a filter element could be inserted into the pressureequalization channel 19, preferably in its hole 20.

To avoid the further danger of adversely affecting the sealing andguidance system, which could occur due to dirt particles which havealready collected on the inside wall of the housing 1, the guide belt 17is made additionally as a stripper element with a structure shownparticularly in FIG. 2. As shown, the base part of the guide belt 17performs the function of the piston guide in interaction with the insidewall of the housing 1, and has a plain compression ring 29 supported inan annular groove 31 machined into the periphery of the piston 3. Theouter annular surface 33 of the plain compression ring 29 forms theguide surface, and is lengthened in the axial direction to form thestripper lip 35. The stripper lip extends over an axial length somewhatgreater than half the axial length of the plain compression ring 29(FIG. 2). As is likewise clearly seen from FIG. 2, the lip 35 tapers,proceeding from its root on the plain compression ring 29, as far as theend edge 37 with a tapering angle α. In the example shown, the angle isapproximately 10 degrees relative to the axial direction. As is likewiseseen from FIG. 2, the radial thickness of the lip 35 on its rootbordering the plain compression ring 29 is somewhat less than half theradial thickness of the plain compression ring 29.

In the guidance and stripper element which forms the guide belt 17, theplain compression ring 29 and the stripper lip 35 are formed integrallyof an elastomer material so that the plain compression ring 29 can besnapped into the annular groove 31 on the piston 3 and the lip 35extends projecting in a flexible manner. As seen in FIG. 1, the lip 35extends over the end-side peripheral section 39 of the piston 3. Thissection extends into the area of the fluid-side end 13, and is somewhatreduced in outside diameter. Due to the intermediate space formed in thesection 39 between the piston 3 and the lip 35, lip 35 can be conformedin an elastically flexible manner to the inside wall of the housing 1,by means of which the lip 35 achieves an optimum stripper action.

Efficient operating behavior can be ensured over a very long servicelife by the configuration of the guidance and sealing system provided inthe present invention. The pressure equalization between the space 23 onthe piston periphery and the fluid side 7 and the measures providedcombine to prevent settling of dirt particles on the inside wall of thehousing 1.

The guide belt 9 is shown on the left as viewed in FIG. 1 can bedesigned comparably to the guide belt 17 shown on the right and/or canbe replaced by it.

While one embodiment has been chosen to illustrate the invention, itwill be understood by those skilled in the art that various changes andmodifications can be made therein without departing from the scope ofthe invention as defined in the appended claims.

1. A hydraulic accumulator, comprising: an accumulator housing extendingalong a longitudinal axis and having a gas side, a fluid side and a sidewall; a piston being movable in said housing along said longitudinalaxis, separating said gas side and said fluid side, and having anannular groove on a periphery thereof and a reduced outside diametersection extending from said annular groove at an end of said pistonadjacent said fluid side; first and second guide elements on saidperiphery of said piston interacting with said side wall of said housingand located adjacent said gas side and said fluid side, respectively,said second guide element being a guide belt with a dirt stripper lipextending at least approximately to an end of said piston and with aplain compression ring sitting in said annular groove, said dirtstripper lip lengthening a radially outside surface of said guide belton one axial end thereof in an axial direction, tapering toward a freeend thereof at a 10° angle relative to said longitudinal axis andextending over said reduced outside diameter section, said compressionring being rectangular in transverse cross-section, said dirt stripperlip having a root adjacent said compression ring with a thickness lessthan one-half a radial thickness of said compression ring; at least onesealing element offset in an axial direction on said periphery of saidpiston from said gas side and being spaced from and between said guideelements; a pressure equalization channel opening on said periphery ofsaid piston between said second guide element and said sealing element,opening on an axial end of said piston on said fluid side, and providingfluid communication therebetween; and a device in said equalizationchannel reducing a cross-sectional area thereof.
 2. A hydraulicaccumulator according to claim 1 wherein said device acts as a particlefilter by dramatically or substantially reducing said cross section ofsaid pressure equalization channel.
 3. A hydraulic accumulator accordingto claim 2 wherein said device is a choke.
 4. A hydraulic accumulatoraccording to claim 3 wherein said choke has a nozzle.
 5. A hydraulicaccumulator according to claim 4 wherein said nozzle is adjacent apiston side at said fluid side, and is inserted into a mouth of saidpressure equalization channel.
 6. A hydraulic accumulator according toclaim 3 wherein said choke is a porous filter element.
 7. A hydraulicaccumulator according to claim 1 wherein said compression ring and saiddirt stripper lip are integrally formed of elastic material.